1. Field of the Invention
This invention relates to switch for keyboard input device, in particular, for a switch suitable for keyboard input device for a portable personal computer such as a note book and mobile type.
2. Related Art
Recently, a demand for miniaturization in thickness of a keyboard input device of a portable personal computer has been more increased, and in response to that demand, for example, in Japanese patent laid-open No. Hei 6-260053, such a keyboard as shown in FIG. 4 is proposed. This is formed by overlapping and fixing a plate-like holder 2 on a flexible circuit board (switch substrate) 1 comprising movable contact and a keycap 4 (hereinafter referred to as "keycap") is provided on a pantograph assembly (guide support member) 3.
The above pantograph assembly 3 comprises two hinge members (movable members) 6, 7, intermediate portions of which are connected in a hinge like so as to form a x figure, and both movable members 6, 7 are at one end thereof supported respectively on a holder 2 and clamping portions 2a, 4a provided on the keycap 4 rotatively, and each other end thereof is supported slidably on sliding stepped portions 4b, 2b provided on the keycap 4 and the holder 2. The keycap 4 is, by receiving a biasing force of a rubber spring 7 surrounding the movable contact through the pantograph assembly 3, normally positioned in an upper elevated position shown in figure, and when the keycap 4 is pushed from this state, the pantograph assembly 3 is folded and the rubber spring 7 is pushed to crush, so that said movable contact is adapted to close. That is, by interposing a pantograph assembly 3 between the holder 2 and the keycap 4, the settling height of the keycap 4 can be made as lower as possible, to that extent, the miniaturization in thickness of the input device for the keyboard can be realized.
By the way, the above key switch including not only the holder 2, but also the keycap 4 and the movable members 6 and 7 have been molded with a resin since the production cost is low and the preferable sliding feeling between the holder 2, the keycap 4 and the pantograph assembly 3 is guaranteed. In this case, since there is a limit of miniaturization in thickness in particular concerning the holder 2 (1 mm is a limitation thereof) due to the strength property or the material conditions at the time of molding, if the clamping portion 2a and the sliding and guiding portion 2b are included, the holder 2 becomes thick as a whole, and as a result, the demand for further miniaturization in thickness can not be responded.
Now, by preparing the holder 2 with a metal it is possible to miniaturize it in thickness, but in that case, due to the metal contact of the two movable members 6, 7 of the pantograph assembly 3 to the holder 2, the sliding feeling property is deteriorated, in addition, it must be necessary to prepare a complicated working to form the clamping portion 2a and the sliding and guiding portion 2b, which causes a production cost to become greatly high and that causes not to reach to a fundamental solution.
The present invention has been made in the light of the above problem, and the purpose thereof is to attain the miniaturization in thickness of the holder without deteriorating the property of the sliding feeling or inviting a great increase in production cost, and thereby to provide a key switch to greatly contribute in miniaturization in thickness of the keyboard input device.